Lease Obligations (Schedule of Future Minimum Lease Commitments) (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Finance Leases
2019, remaining three months	$ 28,500
2020	107,400
2021	93,700
2022	54,900
2023	15,500
Thereafter	500
Total minimum lease payments	300,500
Less amounts representing interest	(18,300)
Total lease obligations, net of interest	282,200
Less current portion	99,300
Long-term portion of lease obligations, net of interest	182,900
Operating Leases
2019, remaining three months	24,300
2020	82,700
2021	59,900
2022	36,400
2023	19,700
Thereafter	40,900
Total minimum lease payments	263,900
Less amounts representing interest	(25,500)
Total lease obligations, net of interest	238,400
Less current portion	79,150	$ 0
Long-term portion of lease obligations, net of interest	$ 159,283	$ 0